Why does this transparent PNG cause borders when combined using GD?

Question

I am trying to create an image from an another image using PHP. Here is my code:

<?php
    $width = 109;
    $height = 109;
    $image = imagecreatetruecolor($width, $height);
    $source_under = imagecreatefrompng('ecloid_under.png');
    $black = imagecolorallocate($image, 0x00, 0x00, 0x00);

    imagecolortransparent($image, $black);

    imagecopy($image, $source_under, 0, 0, 0, 0, $width, $height);

    header('Content-type: image/png');
    imagepng($image);
    imagedestroy($image);
?>

So I am loading this image in $source_under

and copying it over a transparent blank "canvas" image. Here is the result of that operation:

As can be seen, there is a sort of black border around the whole initial image. I think this is due to the fact that initially, the "canvas" image is all black. So there is something wrong with the transparency and the anti-aliasing of the image.

This isn't the first time I have a similar problem, but last time the source image was the cause. This time around, opening it in Photoshop does not show any potential problems with it.

Does anyone know how to fix this?

Answer 1

Can you try to enable alpha blending on $image before you copy the original to it:

imagealphablending($image, true); 

Second try would be to create a transparent color and to fill $image with that color before the copy.

$transparent = imagecolorallocatealpha($image, 0, 0, 0, 127);
imagefill($image, 0, 0, $transparent);
imagealphablending($image, true);